`lateinit` lets you initialize a non-null `var` later (after construction). You can use it only with mutable properties of non-primitive types (not `val`, not `Int`), and you must set it before reading or you’ll get an exception.
Advanced answer
Deep dive
Expanding on the short answer — what usually matters in practice:
Context (tags): lateinit, null-safety, properties
JVM: memory (heap/stack), GC, and what drives latency.
Contracts: equals/hashCode/toString, mutability and consequences.
Explain the "why", not just the "what" (intuition + consequences).
Trade-offs: what you gain/lose (time, memory, complexity, risk).
Edge cases: empty inputs, large inputs, invalid inputs, concurrency.
Examples
A tiny example (an explanation template):
// Example: discuss trade-offs for "what-is-`lateinit`-and-when-can-you-use-it?"
function explain() {
// Start from the core idea:
// `lateinit` lets you initialize a non-null `var` later (after construction). You can use it
}
Common pitfalls
Too generic: no concrete trade-offs or examples.
Mixing average-case and worst-case (e.g., complexity).